Welding in the welding joint cracking caused by, collectively called the weld cracks, welding cracks in the weld metal and heat-affected zone are likely to produce, is solid phase metallurgy metallurgy and welding solidification process in one of the most dangerous defects, welding structure most of the accidents are caused by welding cracks.Avoid welding cracks when there are so many ways, the most common is the material before welding Preheat and post weld cooling, reducing the residual stress in weld zone, due to the latency of crack, until some time after the welding, so emergency heat can reach the goal of preventing cracks.Now most factories adopt electric heating or flame in two ways, but due to the flame of the adaptable, for heating the material more ideal result, many experienced welders started by flame heating for preheating.